Copolymers of ethylene and α-olefins (consisting of 8, 12, 18 or 26 carbons) synthesized with zirco-nocene catalyst (which provided regular comonomer distribution) were investigated by differential canning calorimetry and X-ray scattering. As indicated from the calorimetry and small-angle X-ray scattering, the ethylene-hexacosene copolymer with comonomer content of 3 mol% may have a second crystallites present. As no other reflections were measured with wide-angle X-ray scattering, the side chains crystallites should have the same dimensions of its crystal lattice as the main chain crystalline structures. Since this side chains crystallization was found only in the ethylene-hexacosene copolymer with higher content of comonomer, a critical concentration of sufficiently long comonomer chains should be reached for this secondary crystallite formation.